Method of diametrally expanding an elastic tube

ABSTRACT

A method of diametrally expanding an elastic tube (6), which includes the steps of inserting a distal end portion of a expansion member (1) into an elastic tube (6), the expansion member (1) being provided at least at a surface thereof with a solidified layer of a low melting point material, and the distal end portion (4) of the expansion member (1) being tapered, a tip end of which having a diameter which is equal to or smaller than an inner diameter of the elastic tube (6), and moving the elastic tube (6) over the solidified layer to diametrally expand the elastic tube (6), the surface of the solidified layer being made into a low frictional surface due to a melting of the low melting point material.

FIELD OF THE INVENTION

This invention relates to a method of expanding the diameter of anelastic tube, and in particular to a method of expanding the diameter ofan elastic tube which is adapted to be employed for enclosing the jointportion, for instance of electric wire, cable, pipe, etc.

BACKGROUND INFORMATION

In recent years, there has been developed, for the purpose ofprotecting, insulatively enclosing or repairing a joint portion ofelectric wire, cable, pipe, etc., a method of employing aself-shrinkable elastic tube which is capable of covering the jointportion without necessitating the application of heat in place of theconventional method of using a heat-shrinkable tube. Thisself-shrinkable elastic tube is made of a rubber-like elastic materialand is normally supported in advance on a tubular rigid supporting bodywhereby the inner diameter of the elastic tube is kept in an expandedstate.

In the employment of the self-shrinkable elastic tube, theself-shrinkable elastic tube is inserted over a joint portion of powercable for instance while it is kept in an expanded state as mentionedabove, and then the supporting body is withdrawn from theself-shrinkable elastic tube, thereby allowing the self-shrinkableelastic tube to be shrunk diametrally, thus obtaining the joint portionwhich is hermetically covered by the elastic tube.

There has been conventionally proposed the following method as a meansto expand the diameter of such an elastic tube.

Namely, first of all, an elongated bag-like expandable hollow body twiceas long as that of the self-shrinkable elastic tube is prepared. Then,the fore half portion of this expandable hollow body is inserted intothe self-shrinkable elastic tube, and then the expandable hollow body isentirely expanded by means of a pressurized air whereby diametrallyexpanding the self-shrinkable elastic tube. Thereafter, a supportingbody disposed on the side of the rear half portion of the expandablehollow body is forcibly introduced into the fore half portion of theexpandable hollow body where the self-shrinkable elastic tube isdisposed. Then, the pressurized air in the expandable hollow body iswithdrawn thereby allowing the expandable hollow body to shrink. As aresult, a self-shrinkable elastic tube rested on the supporting bodywith the self-shrinkable elastic tube being kept expanded can beobtained (Japanese Patent Unexamined Publication S/63-74624).

However, this conventional method is accompanied with the problem thatsince a bag-like expandable hollow body is rendered to be interposedbetween a supporting body and a self-shrinkable elastic tube in theprocess of resting the self-shrinkable elastic tube on the supportingbody in this method, the hollow body is ultimately left stronglysandwiched between the supporting body and the self-shrinkable elastictube. As a result, it is very difficult to remove the supporting bodyfrom the self-shrinkable elastic tube at the occasion of mounting theself-shrinkable elastic tube on the joint portion of a power cable forinstance.

OBJECTS AND SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a method ofexpanding the diameter of a self-shrinkable elastic tube, which makes itpossible to easily perform the diametral expanding operation of aself-shrinkable elastic tube.

According to this invention, there is provided a method of diametrallyexpanding an elastic tube, which comprises the steps of:

inserting a distal end portion of an expansion member into an elastictube, the expansion member being provided at least at a surface thereofwith a solidified layer of a low melting point material, and the distalend portion of the expansion member being tapered, a tip end of whichhaving a diameter which is equal to or smaller than an inner diameter ofthe elastic tube; and

moving the elastic tube over the solidified layer to diametrally expandthe elastic tube, the surface of the solidified layer being made into alow frictional surface due to a melting of the low melting pointmaterial.

According to this invention, there is also provided a method ofdiametrally expanding an elastic tube, which comprises the steps of:

inserting a distal end portion of a expansion member into an elastictube; the expansion member being provided at a surface thereof with asolidified layer of a low melting point material and also provided at arearward thereof with a hole for housing a hollow supporting bodytherein; and the distal end portion of the expansion member beingtapered, a tip end of which having a diameter which is equal to orsmaller than an inner diameter of the elastic tube;

moving the elastic tube over the solidified layer to diametrally expandthe elastic tube, the surface of the solidified layer being made into alow frictional surface due to a melting of the low melting pointmaterial; and

allowing the expanded elastic tube to be rested on the hollow supportingbody while withdrawing gradually the hollow supporting body from thehole.

According to this invention, there is further provided a method ofdiametrally expanding an elastic tube, which comprises the steps of:

inserting a distal end portion of a expansion member into an elastictube; the expansion member being provided at least at a surface thereofwith a solidified layer of a low melting point material and alsoprovided rearward therein with a hollow supporting body therein; and thedistal end portion of the expansion member being tapered, a tip end ofwhich having a diameter which is equal to or smaller than an innerdiameter of the elastic tube;

moving the elastic tube over the solidified layer to diametrally expandthe elastic tube, the surface of the solidified layer being made into alow frictional surface due to a melting of the low melting pointmaterial; and

melting and eliminating the low melting point material thereby allowingthe expanded elastic tube to be rested on the hollow supporting body.

As for the low melting point material useful in this invention, there isnot any particular limitation as long as it can be melted within therange of temperature which would not dissolve or denature the materialsconstituting the elastic tube or the hollow supporting body. The meltingpoint of this low melting point material should preferably be -60° C. ormore if the elastic tube is formed of silicone rubber. Because if themelting point of this low melting point material is less than -60° C.,the elastic modulus of silicone rubber would become less than 1 MPa andhence silicone rubber can hardly be deformed.

Preferable examples of the low melting point material are those whichare liquid at normal temperatures, specifically water (melting point: 0°C.), glycerin (melting point: 17° C.), ethylene glycol (melting point:-11.5° C.), etc. Most preferable example of the low melting pointmaterial is water, which can be easily solidified into ice.

For example, an expansion member can be manufactured by solidifyingwater at a temperature of -0° C. to -20° C., and then employed byallowing the ice to melt whereby rendering the surface to become low infriction, thus allowing an elastic tube to be easily slid on the surfaceof the expansion member in the diametral expanding process of theelastic tube. This is one of most important features of this invention.

The tapered angle of the tapered portion of the expansion memberaccording to this invention should preferably be in the range of 5 to 30degrees, i.e. 10 to 60 in apex angle. The tip portion of the expansionmember where the diameter thereof is not larger than the inner diameterof the elastic tube may not be tapered but may be flat-ended. In otherwords, the shape of the tip portion of the expansion member may beoptionally selected as long as it can be inserted into the elastic tube.The diameter of the tip portion of the expansion member is required tobe approximately equal to or smaller than the inner diameter of theelastic tube before the elastic tube is expanded. The expression of"approximately equal to" should be understood to a case where thediameter is slightly larger than the inner diameter of the elastic tube.Because, due to the elasticity of the elastic tube, it is possible toinsert the tip end portion of the expansion member into the elastic tubeeven if the diameter of the tip end of the expansion member is slightlylarger than the inner diameter of the elastic tube.

If the angle of the tapered portion of the expansion member is toolarge, a large force would be required in expanding the diameter of theelastic tube. Moreover, if the angle of the tapered portion of theexpansion member is too large, the difference in angle between thetapered portion and the horizontal portion becomes too large so that anexcessively large force would be required at the moment of transferringthe elastic tube from the tapered portion to the horizontal portion.Therefore, the boundary portion between the tapered portion and thehorizontal portion should preferably be as smooth as possible so as tofacilitate the movement of the elastic tube over the expansion member.

As explained above, it is possible according to this invention tominimize the frictional force even if the hoop stress of the elastictube is increased in the expansion in diameter of the elastic tube.Therefore, the tensile stress in the axial direction can be minimized,and hence there is little possibility that the elastic tube is fracturedin this process of expanding the elastic tube. Accordingly, it ispossible to perform the diametral expansion of the elastic tube withoutgiving a damaging to the. elastic tube.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are respectively a cross-sectional view of an expansionmember to be employed in a method of expanding the diameter of anelastic tube according to a first embodiment of this invention;

FIGS. 2A to 2D are respectively a side view illustrating the process ofexpanding the diameter of an elastic tube according to a firstembodiment of this invention;

FIGS. 3A and 3B are respectively a cross-sectional view showing amodified example of the expansion member to be employed in the method ofexpanding the diameter of an elastic tube according to a firstembodiment of this invention;

FIG. 4 is a cross-sectional view showing an expansion member to beemployed in the method of expanding the diameter of an elastic tubeaccording to a second embodiment of this invention;

FIGS. 5A and 5B are respectively a cross-sectional view showing amodified example of the expansion member to be employed in the method ofdiametrally expanding an elastic tube according to a third embodiment ofthis invention; and

FIGS. 6A to 6E are respectively a cross-sectional view illustrating theprocess of expanding the diameter of an elastic tube according to athird embodiment of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Various embodiments of this invention will be explained with referenceto the drawings as follows.

FIGS. 1A and 1B illustrate a expansion member to be employed in thefirst embodiment of this invention.

As shown in FIG. 1A, the expansion member 1 is placed in a cylindricalcontainer 2 having a conical tip end. In the manufacture of thisexpansion member 1, a low melting point material 3, typically water, ispoured into the container 2. Thereafter, the container 2 is kept in atank which is cooled to a solidification temperature of the low meltingpoint material 3, whereby the low melting point material 3 is solidifiedforming the expansion member 1.

FIG. 1B illustrates the expansion member 1 which has been taken out ofthe container 2. This expansion member 1 is configured to the same shapeas that of the interior of the container 2, and hence constituted by aconical distal end portion 4 and a cylindrical barrel portion 5 havingthe same diameter as that of the maximum diameter of the conical tipportion 4. Since this expansion member 1 is made of the low meltingpoint material 3, the surface thereof melts under normal temperatures,thus making the surface slippery.

The process of expanding the elastic tube 6 by making use of theexpansion member 1 shown in FIG. 1B will be explained with reference toFIGS. 2A to 2D. First of all, as shown in FIG. 2A, the elastic tube 6 isinserted over the distal end portion 4 of the expansion member 1. Then,the elastic tube 6 is shifted from the distal end portion 4 up to thecylindrical barrel portion 5 of the expansion member 1. In this case,since the surface of the expansion member 1 is made slippery by themelting thereof, the elastic tube 6 can be easily moved from the distalend portion 4 to the cylindrical barrel portion 5 as shown in FIGS. 2B,2C and 2D with a weak force. In this manner, the elastic tube 6 can bediametrally expanded.

By the way, the method of moving the elastic tube 6 from the conicaldistal end portion 4 to the cylindrical barrel portion 5 can beperformed by either pushing or pulling the elastic tube 6.

FIGS. 3A and 3B illustrate another example of the expansion member to beemployed in the first embodiment of this invention.

In the example shown in FIG. 3A, the expansion member 1 is constitutedby a core member 7 of small wall thickness and a solidified layer 8formed on the outer surface of the core member 7. Namely, since thesolidified body of a low melting point material is formed into a thinlayer, the quantity of the solidified body can be minimized. As for thematerial for the core member 7, a material which cannot be denatured ordoes not exhibit brittleness in the temperature range of from themelting point of the solidified body to the working temperature, such asmetal, plastics and wood can be employed.

In the example shown in FIG. 3B, the expansion member 1 is constitutedby a solid core member 9 and a solidified layer 10 formed on the outersurface of the core member 9. The shape of the core member 9 is ofstreamline, so that the elastic tube can be easily moved rearward afterit is diametrally expanded. In the case of this expansion member 1, thesurface of the core member 9 should preferably be entirely covered bythe solidified layer 10. However, in view of facilitating the handlingthereof, a portion of the core member 9 may not be covered by thesolidified layer 10 if the elastic tube can be satisfactorily expandeddiametrally. As for the material of the core member 9, metal, plastics,wood, etc. can be employed.

FIG. 4 illustrates the expansion member to be employed in the secondembodiment of this invention. This expansion member 11 is constituted bya core member 12 and a solidified layer 13 formed on.the outer surfaceof the core member 12. The space in the core member 12 of the expansionmember 11 is utilized for housing the hollow supporting body 14. Namely,the rear portion of the core member 12 is elongated as compared with theordinary expansion member, thus making it possible to house the hollowsupporting body 14 for carrying a diametrally expanded elastic tube 16in the hole 15 formed in the core member 12. As for the material of thecore member 21, metal, plastics, wood, etc, can be employed.

This expansion member 11 can be employed as follows. First of all, thehollow supporting body 14 is introduced into the hole 15 of the coremember 12. Then, the distal end portion of the expansion member 11 isfitted in the elastic tube 16. Since the surface of the expansion member11 is slightly melted and made slippery, the elastic tube 16 can beeasily diametrally expanded with a small force and moved to the barrelportion of the expansion member 11. Then, as shown in FIG. 4, a hollowsupporting body 14 housed in the hole 15 is gradually withdrawntherefrom, whereby allowing the elastic tube 16 to be rested on thesurface of the hollow supporting body 14, thus easily manufacturing aself-shrinkable elastic tube.

FIGS. 5A and 5B illustrate the expansion member to be employed in thethird embodiment of this invention. As shown in FIG. 5A, this expansionmember 21 is housed in a cylindrical container 22 having a conical tipend. In the manufacture of this expansion member 21, a hollow supportingbody 23 is temporarily held at a rear portion of the container 22, andthen a low melting point material 24, typically water, is poured intothe container 22. Thereafter, the container 22 is kept in a tank whichis cooled to not more than the solidification temperature of the lowmelting point material 24, whereby the low melting point material 24 issolidified, thus forming the expansion member 21.

FIG. 5B illustrates the expansion member 21 which has been taken out ofthe container 22. This expansion member 21 is configured to the sameshape as that of the interior of the container 22, and hence constitutedby a conical distal end portion 25 and a cylindrical barrel portion 26having the same diameter as that of the maximum diameter of the conicaltip portion 25. Since this expansion member 21 is made of the lowmelting point material 24, the surface thereof melts under normaltemperatures, thus making the surface slippery.

The process of expanding the elastic tube 27 by making use of theexpansion member 21 shown in FIG. 5B will be explained with reference toFIGS. 6A to 6E. First of all, as shown in FIG. 6A, the elastic tube 27is inserted over the distal end portion 25 of the expansion member 21.Then, the elastic tube 27 is shifted from the distal end portion 25 upto the cylindrical barrel portion 26 of the expansion member 21. In thiscase, since the surface of the expansion member 21 is made slippery bythe melting thereof, the elastic tube 27 can be easily moved from thedistal end portion 25 to the cylindrical barrel portion 26 as shown inFIGS. 6B, 6C and 6D with a weak force. As a result, the elastic tube 27is diametrally expanded.

Subsequently, the low melting point material 24 is allowed to melt andeliminated ultimately by heating the expansion member 21 entirely. As aresult, a self-shrinkable elastic tube 27 which is rested on the hollowsupporting body 23 as shown in FIG. 6E. can be obtained.

In this embodiment, the expansion member 21 is fabricated entirely by alow temperature solidification body except the hollow supporting body23. However, most of the portion of solidification body except thesurface portion is not meaningful in carrying this method, so that theportion of solidification body except the surface portion may bereplaced by other materials or an air space so as to reduce the quantityof the low temperature solidification body and to save thesolidification time and handling procedure.

As explained above, according to this invention, since the diametralexpansion of the elastic tube can be performed by taking advantage ofthe low frictional melted surface of the expansion member, it ispossible to minimize the frictional force even if the hoop stress of theelastic tube is increased in the expansion in diameter of the elastictube, and hence the tensile stress in the axial direction can beminimized, thus minimizing any possibility of fracturing the elastictube. Accordingly, it is possible to perform a diametral expansion in amaximum extent irrespective of the wall thickness and diameter of theelastic tube. Further, the diametral expansion of the elastic tube canbe performed by utilizing water which is cheap in price, availableeasily and easy in handling.

According to this invention, since the elastic tube is transferred ontothe hollow supporting body by taking advantage of the low frictionalmelted surface of the expansion member, the tensile stress in the axialdirection at the occasion of the transferring the elastic tube can beminimized, thus minimizing any possibility of fracturing the elastictube. Accordingly, it is possible to perform a diametral expansion in amaximum extent irrespective of the wall thickness and diameter of theelastic tube. It is also possible to efficiently transfer a diametrallyexpanded elastic tube onto a hollow supporting body in a singleprocessing step. Further, the method of this invention is advantageousin that it utilizes water which is cheap in price, available easily andeasy in handling, and also utilizes a cheap housing for hollowsupporting body. Of course, there is not any intervening materialbetween the hollow supporting body and the elastic tube as in the caseof the conventional method.

According to this invention, since the elastic tube is transferred ontothe hollow supporting body by taking advantage of the low frictionalmelted surface of the expansion member with the solidified layer beingultimately eliminated by the melting thereof, the excessive stress to beapplied to the elastic tube can be minimized, thus minimizing anypossibility of fracturing the elastic tube. Accordingly, it is possibleto utilize an elastic tube of fragile but high quality material. Ofcourse, as mentioned above, there is not any intervening materialbetween the hollow supporting body and the elastic tube as in the caseof the conventional method.

What is claimed is:
 1. A method of diametrally expanding an elastictube, which comprises the steps of:introducing a hollow supporting bodyinto a hole for housing said hollow supporting body therein at arearward portion of an expansion member; inserting a distal end portionof said expansion member into an elastic tube, said expansion memberhaving on a surface thereof a solidified layer of water; said distal endportion of said expansion member being tapered, a tip end of which has adiameter which is equal to or smaller than an inner diameter of saidelastic tube; melting a surface of said solidified layer of water tomake said surface of said solidified layer into a low frictionalsurface; moving said elastic tube over said low frictional surface todiametrally expand said elastic tube on said expansion member; andgradually withdrawing said hollow supporting body from said hole therbyallowing said elastic tube to be maintained on an outer surface of saidhollow supporting body.
 2. A method of diametrally expanding an elastictube, which comprises the steps of:encasing or embedding a hollowsupporting body in a rearward portion of a solidified layer of water ofan expansion member; said expansion member having said solidified layerof water on at least a surface thereof; inserting a distal end portionof said expansion member into an elastic tube, said distal end portionof said expansion member being tapered, a tip end of which has adiameter which is equal to or smaller than an inner diameter of saidelastic tube; melting a surface of said solidified layer of water tomake said surface of said solidified layer into a low frictionalsurface; moving said elastic tube over said low frictional surface todiametrally expand said elastic tube on said expansion member; andmelting and eliminating said solidified layer of water in its entiretythereby allowing said expanded elastic tube to be maintained on an outersurface of said hollow supporting body.